Transcript The History of Life

Chapter 17
 Paleontologists – study fossils
 Infer an organism’s structure, diet, and where they lived
 Fossil record – shows how organisms changed over time
 >99% of all species that have ever
lived are extinct (died out)
 Formation – most found in
sedimentary rock
 Particles of rock, sand, and clay are carried
by water and settle at the bottom of oceans
and rivers.
 Organisms that die also sink to the bottom
where they are covered as more rock
material sinks.
 The weight and pressure increase over time
and turn the particles into rock.
 Other fossils are formed when an entire organism is
covered by ice or amber.
 2 techniques to determine age
 Relative dating – look at what layer of strata the fossil is
found in
 Usually deeper = older
 Radioactive dating (absolute dating) – uses the half-life of a
radioactive isotope
 Half-life – amt of time required for ½ the atoms in a radioactive
sample to decay
 Much more accurate
 Ex. Carbon-14 half-life = 5730 years
 Useful for fossils younger than 60,000 years old
 Use potassium-40 (half-life = 1.26 billion years) for older fossils
 Begins with Precambrian Time (650-544 mya)
 Then broken into eras which are then divided into
periods
 Precambrian Time (650-544 mya)
 90% of Earth’s history
 Life existed only in the sea
 544-245 mya – paleo = old; zoic = life
 Cambrian
 Cambrian explosion – diversification of life
 Organisms with hard body parts appeared
 Life still in the ocean
 Ordovician and Silurian
 Invertebrates and plants began to appear on land
 Devonian
 Age of fishes – due to thriving life in the oceans
 Appearance of sharks
 Appearance of insects
 Vertebrates appeared on land
 Carboniferous and Permian
 Life spread out over land.
 Reptiles
 Swampy forests (sediment eventually produced coal)
 Permian Extinction – 95% of life died out
 245-65 mya – Age of Dinosaurs – meso =
middle
 Triassic
 Dinosaurs and mammals appeared
 Jurassic
 Land ruled by dinos
 Archaeopteryx appeared – 1st bird
 Cretaceous
 T-rex
 Flowering plants
 Cretaceous Extinction – death of the
dinos
 50% of life died out
 65-present – Age of Mammals – ceno = recent
 Tertiary
 Whales and dolphins appeared
 Grasses evolved – led to grazing animals
 Quaternary
 Series of ice ages
 Large-scale evolution – 6 patterns of evolution
 Extinctions
 Mass extinctions left habitats wide open for those left to
evolve and fill.
 Ex. Dinosaur extinction allowed mammals to thrive.
 Adaptive radiation
 A species evolves into different forms based on environment.
 Ex. Galapagos finches and tortoises
 Convergent evolution
 Unrelated organisms become similar.
 Ex. Sharks, dolphins, penguins, seals
 Coevolution
 2 species evolve in response to each other over time
 Ex. Orchid and hawk moth
 Ex. Plants have evolved poisons in response to insect attacks
– some insects eventually were able to alter the poison
 Punctuated equilibrium
 Long, stable periods interrupted by brief periods of rapid
change
 Can be caused by:
 Isolation of small portions of the population – changes spread
more quickly with fewer organisms or they evolve to fill all niches
 Mass extinctions – leave open many niches to be filled
 Developmental genes and body plans
 Hox genes – control development of important body
structures
 Turning the genes on/off can produce major changes in body
plan
 Ex. Ancient insects had wings on every segment. Today’s
insects have wings on only 1 or 2 segments.
 Early atmosphere was most likely made up of hydrogen
cyanide, carbon dioxide, carbon monoxide, nitrogen,
hydrogen sulfide, and water.
 Stanley and Urey
 Experimented with the early atmosphere to see if life
could have been produced when electricity and uv
radiation were present.
 Experiment did produce amino acids and nitrogen
bases.
 Protenoid microspheres formed.
 Where encased in a membrane which allowed internal
environment to differ from external.
 Believe RNA was the first genetic material.
 Ancestors of photosynthetic cyanobacteria began to
produce oxygen.
 As the amt in the atmosphere increased many organisms
died.
 Allowed new metabolic pathways to form.
 Eukaryotic cells formed.
 Endosymbiotic theory – prokaryotic cells began to live
symbiotically (each helping the other) and eventually
one cell completely took over the other
 Believe the first organelles were the mitochondria.